Head-up displays have long been used in airplanes to aid the pilots. The HUD reflects information the pilot needs off of a half mirror or the windshield and projects that information at a distance in front of the plane so that the pilot does not have to look into the cockpit to see the information.
More recently, HUDs have been used in automotive applications in which the image is projected up and reflected off of the vehicle front windshield, to appear at a distance in front of the driver in combination with scenery forward of the vehicle. With a HUD in a vehicle, the driver does not have to adjust his/her eyes from the road to read information, such as vehicle speed, which is normally displayed in the vehicle instrument panel.
In designing head-up displays, designers prefer a broad range of available display colors for increased design flexibility. Experience has shown, however, that certain parts of the visible spectrum are preferable in a daytime head-up display projection because they are more visible with the ambient daylight in the background. During night time projections, there is an increased range of colors that are well suited for head-up display projections.
What is desired is a display source for a head-up display that is non-emissive and that is suitable for use of the maximum preferred light spectrum.